This invention relates to methods of making color copies by a thermal color transfer process and more particularly to methods of producing color highlighted original documents from xerographic copies.
The manner of obtaining an electrostaticallly imaged copy is well known in the prior art and may be carried out in several ways; for instance, it is described in U.S. Pats. Nos. 2,397,691 and 2,357,809 to Carlson. The method generally followed comprises: (1) electrostatically charging a photosensitive plate; (2) imaging the charged plate by means of actinic radiation which results in dissipation of the charge in the exposed area and an electrostatic image in the unexposed portions of the plate; (3) developing the latent electrostatic image with a pigmented resin powder carrying an opposite electrostatic charge to that on the latent images whereby the powder is attracted and held in image form on the charged area; (4) transferring the image from the imaged plate to a copy sheet by mechanical or electrical means; and (5) fixing the powdered image on the copy sheet by means of heat or chemical treatment.
In U.S. Pat. No. 3,057,720 to Hayford et al., a method for xerographic color reproduction is disclosed. In xerographic reproduction the same basic xerographic steps as outlined above are utilized in combination with the well known subtractive principle of mixing primary colors. According to this principle, three primary colors; namely, green, red and blue, are reproduced by mixtures of the three complementary colors, referred to as subtractive primary colors; namely, magenta, cyan and yellow. According to this subtractive system, a magenta colored material is characterized by a substantially complete absorption of the primary color green and thus may be designated as green negative; cyan material characterized by substantially complete absorption of the color red; and a yellow material is characterized by a substantially complete absorption of the primary color blue. Utilizing this principle along with the basic xerographic process outlined above, three primary color exposures and three complementary color developments in registration will result in a full-color xerographic reproduction. This process is more fully outlined in the subject patent to Hayford et al.
The introduction of color xerography has made the production of color copy possible. Therefore, the option of reproducing a color original or making a color copy by limiting or changing development sequence are both possible. Therefore, a typewritten letter may be copied to have the typed characters appear green, red or blue. However, the only means presently available for reproducing some designated portion of an original in color (i.e., highlighting) is to have a color highlighted original. In the case of typewritten letter copy, this is significantly difficult and cumbersome inasmuch as certain letters or words would have to be typed in a color while others appear black and white.
Generally, the formation of color highlighted originals for use in color xerographic reproduction processes requires some means of transferring color to a given area of a document. In the case of a typewritten page, a transfer sheet, in the form of a tape or strip, having a flexible foundation and a coating of transferable material comprising essentially a wax-like vehicle having suspended therein a colorant and the original sheet are superimposed and subjected to a localized imaging force in the form of pressure or heat. When using a stripping material having a sheet of a transferable color composition, there is difficulty in isolating compatible and discrimminating materials which will color designate or print portions as desired. Otherwise, the color portions will transfer to undesirable areas such as the background area of a letter. In the case of a typewritter force utilizing a tape, such a procedure is cumbersome and time consuming.
The present invention relates to a color producing material employed to highlight image portions of a xerographic copy so that a color highlight original is available for xerographic color reproduction.